Preparation And Application Of Humidity Sensing Composites Based On Metal Oxides

The measurement and control of humidity is important in many areas such as industrial and agricultural production,domestic environment,food production.The preparation of humidity sensitive materials with potential humidity-sensitive performance plays a significant role in the development of new humidity sensors.Among these humidity sensing materials,metal oxides have attracted considerable attention with typical advantages of simple production,low cost and high humidity sensitivity.However,metal oxides also show intrinsic shortcoming,for example,long response time.In our work,to improve the humidity performance of metal oxide regarding to the response time,several approaches including making composites,doping with humidity sensing elements,designing special structures have been applied.And two types of composites have been prepared,which are CdO/Al2O3 composite and Li+-doped ZnO.1.CdO/Al2O3 composite prepared by calcination of CdAl layered double hydroxides:CdO/Al2O3 composite has prepared by calcination process of sodium dodecyl sulfonate co-intercalated(SDS)Cd,A1 layered double hydroxide(CdAl-LDH)at different temperatures,which has been synthesized by traditional method of hydrothermal synthesis.The composite calcined at 500?(Cd0/Al2O3-500)shows relatively better humidity-sensing performance,such as rapid response time,due to its sheet structure and large surface area..The humidity sensing properties of the sensors based on Cd0/Al2O3-500 not only exhibits a good linearity,small hysteresis and high humidity sensitivity but also shows rapid response and recovery time.The humidity sensing performance is much better than that of CdO&Al2O3-500,which was obtained by calcination of the blended inorganic salts.2.Li+-doped ZnO multistage structured nanosheet:pure ZnO multistage structured nanosheet material and Li+-doped ZnO multistage structured nanosheet material have been prepared by simple hydrothermal method.The results indicate that Li+-doped ZnO shows excellent humidity properties compared with pure ZnO,especially in the response-recovery time.With the increase of Li+ doping content,the absorption performance of water becomes easier and the desorption performance of water becomes slower.So among the materials of Li+-doped ZnO,the ZnO/0.36%Li(ZnO:Li(mol)=1:0.36%),in which the Li+ content is 0.1488 g exhibit the best humidity-sensitive properties.When RH(relative humidity)increases from 11%to 95%RH,the impedance decrease rapidly as soon as 14 s and increases as soon as 11 s by 4 orders.It is believed that LiCl plays a positive effect in humidity properties,whichwould be ionized to Li+.And the dissociated Li+ could play the roles of conduction carriers which could transfer freely.The quick transference of ions on the water layer results in a sharp decrease of impedance of the sensor with near 3.5 orders of magnitude compared to the initial impedance.